Many photographers use digital cameras to capture images. Unlike conventional wet processing of silver halide film and papers, digital images can be printed directly onto sheets of paper. Color images can be printed using ink jet printers, multicolor transferable toner printers, heat sensitive coated paper printers, or thermal dye transfer printers. Many mass-market retail establishments have user-friendly kiosks where shoppers can make color prints. A large number of these kiosks use thermal dye transfer printers. Because the kiosks use large amounts of paper, such kiosks often use a continuous web of paper for printing such images. The images are later separated from each other and from the web by a suitable cutter or knife. In such kiosk printers, the cutting process is typically performed in a manner that ensures that the printed images provided to the user have dye images extend to the edges of the print in both the latitudinal and longitudinal directions. These prints are known as borderless prints and are the most popular prints.
Thermal dye transfer printers generate very high quality images. As such, a number of photographers want their own thermal dye transfer printer. However, it is impractical and not cost effective to supply continuous web paper for use in home printing. It is also expensive to supply built-in paper cutters and knives to provide borderless prints. To attempt to meet the demand for borderless prints, there are known methods of extending the latitudinal edges so that there is no border on the tops and bottoms of prints. See, for example, U.S. Pat. Nos. 5,441,353; 5,196,863; and 5,499,880. However, those techniques cannot provide prints that extend to the longitudinal borders.
One approach to providing borderless prints in a sheet fed thermal printer is modeled after the technique used by home printers. In this approach receiver sheets are provided that are pre-perforated at a distance from each longitudinal edge. FIG. 1 shows a prior art thermal dye transfer printer 2 that is intended to provide monotone, multi-tone or full color borderless printing using a perforated sheet 4 is shown in FIG. 1. Printer 2 records images on a sheet 4 that is driven along a print path by a pair of pinch rollers 6a and 6b connected to a motor 7. A print head 8 is located opposite a free spinning platen 10 through which sheet 4 is passed during printing. Donor take-up roller 12 and donor supply roller 14 support a donor web 16 of thermal dye donor material and are positioned on opposite sides of print head 8 so that donor web 16 passes between print head 8 and platen 10. A bias spring 18 presses print head 8 against donor web 16 to urge donor web 16 against platen 10.
Prior to printing, a leading edge 4.1 of sheet 4 is fed between rollers 6a and 6b. Rollers 6a and 6b pull sheet 4 and donor web 16 between thermal print head 8 and platen 10 where thermal print head 8 causes donor material to be transferred to sheet 4.
Sheet 4 is perforated to provide a separable perforated leading portion 4.1 and a trailing portion 4.3 bordering a central portion 4.2. Donor material, such as a dye, is transferred to sheet 4 such that an image is formed that causes the entire central portion 4.2 and that optionally extends to leading portion 4.1 and trailing portion 4.3 slightly beyond the perforations. When leading portion 4.1 and trailing portion 4.3 are removed at the perforations, central portion 4.2 bears a printed image that extends from edge to edge, and the print appears to be borderless.
A key drawback of this solution is the requirement for special paper with perforations on the leading and trailing edges. Such paper is expensive to manufacture and has little or no other market outside of printing digital images. In addition, customers can be dissatisfied with the requirement of tearing off the perforated edges of the printed images.
Another approach to providing borderless sheet fed prints is to provide a thermal printer with systems that precisely detect the leading edge of a sheet 4 and that precisely positions a leading edge of a sheet at a print head. However, it will be understood that print lines in thermal printers can be arranged on the order of 300 or more lines per longitudinal inch of a sheet. It also will be understood that even a minor border on the order one print line will not be acceptable as a borderless print. This requires that the sensing and positioning equipment in the thermal printer be very precise, thus raising the cost of the printer.
Further, it will be understood that even minor variations in a length of sheet 4, in the sheet transport systems used to position sheet 4 for printing, or in the equipment used to sense the position of sheet 4 can allow for a portion of sheet 4 to be advanced past print head 8 such that a border will appear. Such variations can also cause the leading longitudinal edge to be positioned before the print head such that the printer will begin printing before the longitudinal edge is positioned to receive the print. When this occurs, the leading edge longitudinal edge will appear to be borderless, however, because the printer begins printing without the leading edge at the print head and because the printer will print a predefined length, this problem creates a risk that the printer will stop printing before the trailing edge of the sheet has reached the print head thus creating a border at a trailing edge.
What is needed therefore is a printer and a method for printing that can achieve borderless printing without requiring the use of tear off receiver medium and/or slitting without precision sensing and positioning, and without a border. Such a system should be inexpensive and highly reliable.